AMD GPU Rendering R7 Series
My previous card was a R7 200 series, my actual card is a R9 200 series. While both cards actually seem to work with Blender, there are two major drawbacks. 


The actual driver is faulty and renders "TV stripes" into your image (see https://community.amd.com/thread/198677) 
Blender's development team (like many others) sadly seems to focus on NVIDIA, thus AMD GPU (OpenCL) rendering is not that optimized than NVIDIA's (CUDA) (see https://www.phoronix.com/scan.php?page=news_item&amp;px=Blender-Slow-OpenCL-AMDGPU)


Even with the "good" drivers I haven't experienced much faster rendering. 

Update: I just tested the current driver hotfix 16.8.1 under Windows 7. They seem to work significantly faster and also the "TV stripes" seem to be gone. Linux test might follow by the end of the week.